This grant is requested to support a basic research program aimed at elucidating at the molecular level the nature, mode of functioning and mechanisms of regulation of the specific receptors for dopamine. Physiologically, dopamine exerts effects such as regulation of hormone synthesis and release (prolaction, alpha-melanocyte stimulating hormone and parathyroid hormone) in the periphery and control of behavioral and motor functions in the central nervous system (CNS). These effects are mediated by two distinct receptors (D1 and D2) which are coupled to stimulation (D1) and inhibition (D2) of adenylate cyclase as well as inhibition (D2) of the phosphatidylinositol/calcium signal transfer system. To accomplish the four specific goals of this proposal, studies will be conducted using three main approaches 1) to obtain detaled molecular information about the nature of D1 and D2-receptors we will purify and characterize these proteins from bovine anterior pituitary and corpus straiatum, by newly developed methods of affinity chromatography and affinity and photoaffinity labeling. 2) to understand the way in which agonist occupancy of receptors is translated into the generation of an intracellular signal and the relationship of this signal to the physiological response we will identify the components involved in these systems and perform reconstitution studies with purified components. The D2-receptor represent a unique model to study the relationship between signal transduction systems since this receptor can presumably couple to two signal transfer systems within the same cell. 3) In order to elucidate the biochemical mechanisms by which the function of these receptors might be modulated in vivo, we will examine the receptor-effector coupling in whole cells and reconsitituted systems after treatment of animals or cells with dopamine agonists, neuroleptics and steroids, agents known to modulate dopaminergic responsiveness in target tissues. These studies should provide the complete elucidation of the biochemical nature of these receptors and the mechanisms of signal transduction as well as the mechanisms by which responsiveness of target tissues is controlled. Modulation of dopaminergic responsiveness appears to be an important factor in the control of pituitary function (hyperprolactinemia/amenorrhea) as well as the normal functioning of CNS behaviour and motor functions (schizophrenia, Parkinsons disease and tardive dyskinesia). This project constitutes an integral part of the overall long term objective of this laboratory to characterize at the molecular level the various receptors for catecholamines.